Purification of hydrochloric acid solutions



United States Patent '0 PURIFICATION OF HY DROCHLORIC ACID SOLUTIONSFrancis X. McGarvey, Haddon Heights, N. J., assignor to Rohm & HaasCompany, Philadelphia, Pa., 2 corporation of Delaware No Drawing.Application October 5, 1951, Serial No. 250,040

2 Claims. (Cl. 210--24) This invention relates to the purification ofhydrochloric acid. More particularly it relates to a process of removingdissolved iron impurities from relatively concentrated hydrochloric acidby means of ion-exchange I'GSIDS.

The process is a cyclic one and it comprises treating a hydrochloricacid solution which has a molar concentration of at least siX and whichcontains dissolved iron with an insoluble, strongly basic anion-exchangeresin of which the polar, ion-adsorbing groups are quaternary ammoniumchloride groups, then separating the resin and the acid solution andfinally regenerating the resin by washing it with water in an amountequal to at least ninety per cent of the volume of the resin.

The process can be carried out by merely agitating a mixture of resinand the hydrochloric acid and thereafter separating the two mechanicallyby such methods as decantation and filtration. It is much preferred,however, to pass the contaminated acid solution through a bed or columnof particles of the resin until the resin has adsorbed its capacity ofthe iron impurities; i. e., until the resin has become exhausted. Ineither case the resin, after being separated from the purified acidsolution, is then freed of the adsorbed iron impurities by washing withwater. The resin is thus regenerated and is in condition for re-usewhile the iron impurities are flushed from the resin and are obtained inthe form of a highly concentrated solution from which iron can bereadily recovered.

In this process the concentration of the hydrochloric acid solution iscritical and it must be at least six molar. Iron is not removedefiiciently or at all from solutions which are more dilute.

The iron which is removed is in the ferric state of valence. Any ferrousiron which is to be removed is oxidized to the ferric state before theacid solution is treated with the resin.

The anion-exchange resins which are employed are those which are of thestrongly basic type by virtue of the presence in the molecular structureof the resins of polar quarternary ammonium groups. For purposes of thisinvention the polar groups are quaternary ammonium chloride groups. Itis preferred to start the process with a resin which is in the chlorideform; but it is also to be noted that a resin in any other form, such asthe hydroxyl form or the sulfate form, can be used since it isimmediately converted to the chloride form when brought into contactwith the hydrochloric acid, and remains in the chloride form during theperiod of adsorption and after regeneration with water.

Suitable quaternary ammonium anion-exchange resins include those whichare described in C. H. McBurneys application for Letters Patent, SerialNo. 759,308, filed July 5, 1947, now Patent No. 2,591,573. Such resinsare insoluble, cross-linked copolymers of a monovinyl hydrocarbon,preferably styrene, and a polyvinyl hydrocarbon, preferablydivinylbenzene, to the aromatic nuclei of which are attached throughmethylene groups the polar quaternary ammonium groups. Typical of suchresins are those made by chloromethylating an insoluble copolymer ofabout 92-99.5% styrene and 05-55% divinylbenzene and then reacting thechloromethylated copolymer with a tertiary amine such as trimethylamine,dimethylaminoethanol, dimethylbenzylamine, dimethylaniline,dibenzylmethylamine and the like.

Another type of suitable quaternary ammonium anionexchange resin isdescribed in U. S. Patent No. 2,567,836

Patented-Nov. .30, 1954 2 of'Se'ptemberll, 1951. This -particular kindofresinds made by reacting anacrylamidocompound with-'anallt'ylenedihalide whereby theamino-groups'in'the acryla'mido compound arequaternizedv Still another suitable type is that described in J. C. Hwasapplication for Letters Patent, Serial No. 250,037, filed October 5,1951, now U. S. Patent 2,630,427. This type'is made by reacting in anaqueous medium a tertiary amine, such as those described above, with across-linked, insoluble polymer of a glycidyl ester of acrylic acid orof an alpha-substituted acrylic acid in which the alphasubstituents area chlorine atom or a lower alkyl group.

All of the operable resins, regardless of the process of theirmanufacture are insoluble and contain, as their polar, ion-adsorbinggroups, quaternary ammonium groups attached to a cross-linked, insolublepolymer.

The exhausted resin is regenerated by washing it with water. It isessential that sufiicient water be used, and the minimum volume of watermust be at least of the volume of the resin which is being regenerated.Larger volumes are recommended of the order of two to ten times thevolume of the resin. The resin is, of course, completely regeneratedwhen the last bit of wash water fails to show a test for iron.

The following example serves to illustrate this invention:

A glass cylinder was filled with 4130 cubic centimeters of the particlesof a commercially available anionexchange resin. This resin was made byfirst copolymerizing in suspension a mixture of 96% styrene and 4% ofdivinylbenzene, chloromethylating the insoluble copolymer, then reactingthe intermediate, chloromethylated resin with dimethylaminoethanol,(CH3)zN-C2H4OH, and finally washing the product with an excess of dilutehydrochloric acid. As a result of the method of its manufacture, theresin contained as its polar, anionexchanging groups and quaternaryammonium groups of the formula attached to the aromatic nuclei of themacromolecules.

Through this column were passed three carboys of concentratedhydrochloric acid (32%) containing 0.0022% of dissolved iron and havinga color, on the ApHA scale, of over 200. After passage through thecolumn the acid had an iron-content of only 0.00005 iron and an ApHAcolor of 25. Thus the acid was substantially freed of iron. The rate offlow, within reasonable limits, did not affect the quality of theefiluent and a flow-rate of at least one gallon per minute per cubicfoot of resin was practical.

Although the treatment of three carboys of acid did not exhaust theresin, the latter was regenerated by passage through it of eight litersof water. This amount of water measured a little less than twice thevolume of the column of resin, but was sufiicient to remove over 99% ofthe adsorbed iron as evidenced by analysis of the wash-water.

I claim:

1. A cyclic process for the removal of dissolved ferric iron impuritiesfrom hydrochloric acid having a concentration of at least six molarwhich comprises treating said hydrochloric acid containing said ironimpurities with an anion-exchange resin containing quaternary ammoniumchloride groups as its polar groups, separating said resin and saidhydrochloric acid and regenerating said resin by washing it with avolume of water equal to at least 90% of the volume of said resin.

2. A cyclic process for the removal of dissolved ferric iron impuritiesfrom hydrochloric acid having a concentration of at least six molarwhich comprises treating said hydrochloric acid containing said ironimpurities with an anion-exchange resin containing quaternary ammoniumchloride groups as its polar groups, separating said resin and saidhydrochloric acid and regenerating said resin by washing it with avolume of water equal to two to ten times the volume of said resin.

(References on following page) References Cited in the file of thispatent OTHER REFERENCES UNITED STATES PATENTS Industrial and EngineeringChemistry, vol. 35, No. 8, Number Name Date g- 1943, PP-

2,104,501 Adams et a1 Jan. 4, 1938 I Industrial and EngmeeringChemistry, vol. 37, No. 7, 2,105,700 Ramage Jan. 18, 1938 July 1945, pp.618-624. 2,258,216 Ramage Oct. 7, 1941 2,567,836 Anthes Sept. 11, 1951

1. A CYCLIC PROCESS FOR THE REMOVAL OF DISSOLVED FERRIC IRON IMPURITIESFROM HYDROCHLORIC ACID HAVING A CONCENTRATION OF AT LEAST SIX MOLARSWHICH COMPRISES TREATING SAID HYDROCHLORIC ACID CONTAINING SAID IRONIMPURITIES WITH AN ANION-EXCHANGE RESIN CONTAINING QUATERNARY AMMONIUMCHLORIDE GROUPS AS ITS POLAR GROUPS, SEPARATING SAID RESIN AND SAIDHYDROCHLORIC ACID AND REGENERATING SAID RESIN BY WASHING IT WITH AVOLUME OF WATER EQUAL TO AT LEAST 90% OF THE VOLUME OF SAID RESIN.